Friday, November 02, 2012

The Latest Sunrise of the Year

I pay more attention to this than most, because the viability of bicycling to work depends on when sunrise is. Fact is, this week - the last week of Daylight Saving Time - might actually be the worst week of the year for me to bicycle commute, because this week also has the latest sunrises of the year. Tomorrow in Durham, the sun will rise at 7:41 AM, but during Standard Time, sunrise only gets as late as 7:27 AM (source). That makes tomorrow the latest sunrise of the year, before Standard Time kicks in and sends sunrise back an hour the next morning.

That got me thinking: where else is the latest sunrise of the year not around the Winter Solstice, but on the last day of Daylight Saving Time? Or, to put it another way: how far north do you have to go in order to lose another 60 minutes of morning daylight between now and the end of December? (In Durham, we're only going to lose another 44 minutes.)

Well...turns out, you have to go north of 47°N before the dead of Winter overtakes the last day of Daylight Saving Time for "latest sunrise of the year" honors. For instance, in Seattle (located at 47°38'N),
tomorrow's sunrise is 7:57 AM, but on New Year's Day, sunrise will be 7:58 AM. Go a little further south to Tacoma (47°14'N), and tomorrow is one of many days (the others of which are in December/January) tied for the earliest sunrise of the year. But everywhere south of 47°N (approximately), the latest sunrise of the year will be tomorrow*.

Other cities in this "buffer zone" just north of 47°N, where you lose exactly 60 more minutes of morning daylight, include: Fort Kent, ME; Houghton, MI; Bemidji, MN; and Great Falls, MT. However...next year, it'll be completely different! In 2013, the last day of Daylight Saving Time will be November 2nd instead of November 3rd, and that will push the "buffer zone" a half degree or so south. But as long as Daylight Saving Time ends in the first weekend of November, if you live south of 45°N, the latest sunrise of the year should always fall on the last day of Daylight Saving Time*.

(* - This is all provided your state actually observes Daylight Saving Time, of course.)